Several of the collagen diseases are strongly suspected of being caused by chronic infection although evidence for this remains inconclusive. It is proposed to extend application of several techniques of nucleic acid hybridization as previously developed in this laboratory to the examination of nucleic acids isolated from tissue or plasma from patients with SLE or RA in order to attempt to demonstrate the presence of nucleic adid base sequences of micro-organisms that have been proposed as etiologic agents. Additional studies of the significance of circulating DNA in a variety of collagen disorders and of antibody to native DNA in SLE will also be continued.